5 Cardio Myths that Need to Go Away!

A few months back, I wrote a great post on some of the top strength training fallacies that I hear all the time. Today, I figured I’d go back to myth busting and share some of the top cardio myths that I hear – and hit ya with the truth!

Myth 1: When you’re on a cardio machine, your heart rate should stay in the “fat burning zone” in order to lose weight.

Nope. This is an incredibly prevalent myth that stems from a misunderstanding of exercise science. When you exercise, your body always burns a combination of fat and carbohydrate. At lower intensities, your body burns more fat; at higher intensities, you burn more carbohydrate. However, it’s the total calorie burn – not whether those calories come from carbs or fat – that impact weight loss in the long run. Staying in the “fat burning zone” often leads people to work out at low intensities and because of that, they don’t work as hard and burn fewer calories – slowing their overall progress.

Myth 2: If you can’t get a full hour of cardio, you might as well just skip it.

I think so many people have an all or nothing mentality when it comes to exercise (or other wellness goals). We either want to kill it by drinking a green smoothie for breakfast and getting in two hours at the gym and meditating at home…OR we feel crappy that we ate a donut, decide to skip the gym because “I’d only have 20 minute anyway”, and then zone out in front of the TV. Being fit and healthy means balance – nothing will always fall into place perfectly, and that’s OK. Any exercise is better than nothing. And with HIIT training, you can often get a great workout in those 20 minutes.

Even if you don’t like HIIT, there are still benefits to moderate intensity steady state exercise in short amounts. An interesting study came out of Japan in the late ‘90s that looked at the duration of walks to work and compared it to blood pressure risk. An 11-20 minute daily walk reduced the risk of high blood pressure by 12%, while a walk over 21 minutes reduced the risk by 29%. This is amazing and all the more reason to get some exercise, even if you feel like you can’t fit in a full workout or meet the national recommendations. Little bits of exercise still help your body. {Keep in mind to achieve certain goals however – like weight loss or improved athletic performance – you may need to add additional time to your workouts.}

Myth 3: You should do fasting exercise to burn more fat and lose weight!

OK, the first part of this myth about burning fat is technically true from a biochemistry standpoint, but is usually misunderstood at a practical level. When you do not eat breakfast before exercising, you typically burn a higher percentage of calories from fat versus carbohydrate. Similar to what I mentioned in the fat burning zone myth, your concern for weight loss should be the total result of exercise (i.e. total calorie burn rather than worrying about where those calories are being burned). If you skip eating before a workout and you can’t maintain the same intensity and/or duration of the workout – that leads to a less effective workout overall which is no good.

If you currently work out without eating and feel fatigued more quickly, start having a small meal or snack 1-2 hours before you hit the gym. Along the same lines, if you feel better working out fasted and can maintain the same intensity and duration during short workouts, than that’s fine too.

Now, a quick side note – if you’re an endurance athlete thinking about doing fasted cardio for possible metabolic enhancement/fat adaptation, that’s another conversation. I typically don’t recommend these for recreational athletes, but there may be some biochemical benefits if you’re a competitive athlete and are trying to enhance the fat/carbohydrate ratio of fuel burned (so that you can last longer in endurance events before hitting the wall). That said, this is a complex training method with some risks that requires specific considerations – I recommend consulting with a sports RD or coach on it!

In the fitness world, it seems like we are polarized into two groups – those who think strength training is the fitness panacea and those that think cardio is. The real answer is that it depends on your goals. Fitness does not have to have the same exact definition to every person. You want to structure your workouts focusing on what’s most important to you, as you’ll be able to put your best effort into those. If your goal is building muscle, you’ll have a fitness plan that is more highly strength based than for those training for their next marathon. Ideally for overall health and wellness, everyone will include some mixture of BOTH types – but the specific ratios will vary based on your goals and preferences.

Myth 5: If you do a lot of cardio, you don’t have to worry about your diet.

Goodness gracious, I wish this was true – I’d be eating way more oreos. 🙂 While you do have somewhat more flexibility in the amounts you eat and probably a little more leeway for some occasional treats, your overall meal plan should still be relatively consistent. You want to be fueling your body with lots of vegetables and fruits, lean proteins, whole grains & healthy fats. A lot of cardio tends to increase our appetite (fellow endurance athletes, I’m sure you know what I’m talking about!) so it’s still important to pay attention to portions and food quality.

Share with me: Did any of these myths surprise you? Do you agree or disagree with these? Are there other cardio myths you have heard?

Chrissy Carroll is a Registered Dietitian and USAT Level I Triathlon Coach. She specializes in sharing nutrition and fitness tips, as well as recipes, for runners, triathletes, and active women.Chrissy holds a Bachelor's Degree in Nutrition, a Masters Degree in Public Health, and is also an ACSM Certified Personal Trainer.

It’s definitely important to get both strength training and cardio into your fitness routine. And I’ve had the experience of heading out for a long run without drinking my protein shake with banana a little while beforehand.. Man, did my endurance suffer. Lesson learned!

Good article, you’re presenting the right perspective on cardio exercise — you can’t hack any aspect of it, CICO always catches up in the end. Your points match what I’ve experienced in the last 3 years, losing 27 kg, and keeping it off through cycling and diet!

Yes to everything in this post! We covered every single point you brought up in my exercise physiology class last semester. There’s so much incorrect info online when it comes to fitness, it’s great to see someone get it right!